NDLI: Effect of Elevated Free-Stream Turbulence on Transitional Heat Transfer Over Dual-Scaled Rough Surfaces

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Wang, Ting Matthew, C. Rice
Copyright Year	2003
Abstract	The surface roughness over a serviced turbine airfoil is usually multi-scaled with varying features that are difficult to be universally characterized. However, it was previously discovered in low freestream turbulence conditions that the height of larger roughness produces separation and vortex shedding, which trigger early transition and exert a dominant effect on flow pattern and heat transfer. The geometry of the roughness and smaller roughness scales played secondary roles. This paper extends the previous study to elevated turbulence conditions with free-stream turbulence intensity ranging from 0.2–6.0 percent. A simplified test condition on a flat plate is conducted with two discrete regions having different surface roughness. The leading edge roughness is comprised of a sandpaper strip or a single cylinder. The downstream surface is either smooth or covered with sandpaper of grit sizes ranging from 100 ∼ 40 (Ra = 37 ∼ 119 μm). Hot wire measurements are conducted in the boundary layer to study the flow structure. The results of this study verify that the height of the largest-scale roughness triggers an earlier transition even under elevated turbulence conditions and exerts a more dominant effect on flow and heat transfer than does the geometry of the roughness. Heat transfer enhancements of about 30 ∼ 40 percent over the entire test surface are observed. The vortical motion, generated by the backward facing step at the joint of two roughness regions, is believed to significantly increase momentum transport across the boundary layer and bring the elevated turbulence from the freestream towards the wall. No such long-lasting heat transfer phenomenon is observed in low FSTI cases even though vortex shedding also exists in the low turbulence cases. The heat transfer enhancement decreases, instead of increases, as the downstream roughness height increases.
Sponsorship	International Gas Turbine Institute
Starting Page	871
Ending Page	882
Page Count	12
File Format	PDF
ISBN	0791836886
DOI	10.1115/GT2003-38835
e-ISBN	0791836711
Volume Number	Volume 5: Turbo Expo 2003, Parts A and B
Conference Proceedings	ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference
Language	English
Publisher Date	2003-06-16
Publisher Place	Atlanta, Georgia, USA
Access Restriction	Subscribed
Subject Keyword	Strips Turbulence Vortex shedding Flat plates Airfoils Momentum Surface roughness Separation (technology) Wire Flow (dynamics) Geometry Vortex motion Heat transfer Boundary layers Turbines Cylinders
Content Type	Text
Resource Type	Article

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Effects of Leading-Edge Roughness on Fluid Flow and Heat Transfer in the Transitional Boundary Layer Over a Flat Plate

Effect of Elevated Free-Stream Turbulence on Transitional Flow Heat Transfer Over Dual-Scaled Rough Surfaces

Numerical Study of Transitional Rough Wall Boundary Layer

Extended Models for Transitional Rough Wall Boundary Layers With Heat Transfer: Part I—Model Formulations

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Effect of Two-Scale Roughness on Boundary Layer Transition Over a Heated Flat Plate: Part 1—Surface Heat Transfer

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